In Phase I we showed the feasibility of a Self-Contained Breathing Apparatus (SCBA) that uses liquefied air as a source of breathing air. The health and safety of fire fighters, rescue workers, and personnel in hazardous materials operation is critically dependent on SCBAs. Liquefied air enables an extremely compact, lightweight, open-circuit SCBA that supplies the user with a continuous stream of cool, fresh air and also provides a potent heat sink for body cooling. The innovation is a phase separator that contains the liquefied air and provides vapor to the user with a constant fraction of oxygen, regardless of the fill level of the SCBA or its orientation. In Phase I we proved the key operating principle by demonstrating operation of a model cryogenic phase separator. In Phase II we will develop the SCBA technology to the point of commercialization by (l) development and testing of phase separators for the SCBA, (2) design and development of the entire SCBA system, including control and regulator systems, (3) assembly of prototype SCBAs, and (4) prototype testing at Creare and in the laboratories of our commercial partners. PROPOSED COMMERCIAL APPLICATION: The liquid-air SCBA is an ideal air supply for fire fighters; high-rise, mine, and subway rescue teams; and military fire fighting personnel because it is compact, can be conformal in shape, has a long duration, is lightweight, and open circuit. Liquid- air SCBAs are also very attractive for use in hazardous material operations because the small conformal tank fits well inside anti- contamination suits; the potential for body cooling can make the user much more comfortable.